Field of the Invention
This invention generally relates to a bicycle crank assembly. More specifically, the present invention relates to a bicycle crank assembly having an attachment structure for attaching a pair of sprockets to a crank arm.
Background Information
Generally speaking, a conventional bicycle has a diamond-shaped bicycle frame with a pair of wheels rotatably mounted to the frame and a drive train coupled to the frame for driving the rear wheel. The drive train typically has a bicycle crank assembly mounted to the cylindrical or tubular hanger part of the bicycle frame. The bicycle crank assembly drives a chain that rotates a sprocket mounted to the rear wheel. The bicycle crank assembly usually includes a crank axle that is mounted in a freely rotatable-manner to a hanger tube of the bicycle frame. A crank arm is fastened to each end of the crank axle. The right crank arm typically has one or more sprockets attached thereto for driving the chain. As used herein, the terms “right” and “left” are often used to describe bicycle components on the assumption that the bicycle is viewed from the rear. The sprockets are sometimes attached the right crank arm by a plurality of fixing bolts and a plurality of fixing nuts as shown in U.S. Pat. No. 7,258,041 (assigned to Shimano Inc.). In this conventional bicycle crank assembly, the sprockets are, in an assembled state, directly disposed on a fixing bolt or a fixing nut which is detachable from the sprockets and the right crank arm. The center axes of the fixing bolts can easily become inclined with respect to the center axes of the fixing nuts during attachment of the sprockets to the crank arm, as a result it can be difficult and/or time consuming to accurately position sprockets on the crank arm.